The present invention relates to a means for attachment of intraoral dental or orthodontic force modules, which are used to correct or maintain the position of the upper teeth and or jaws relative to the lower teeth and or jaws.
It is generally known in the field of dentistry, and in particular the specialty of orthodontics, to utilize rigid, one-piece or telescoping devices to position the jaws in a more favorable relation to each other or to deliver tooth moving forces between the jaws. The telescoping devices are either pushrod-and-cylinder or cylinder-within-cylinder type devices. Interarch devices are fixed directly or indirectly to devices such as orthodontic braces or are fixed to removable plates that are in turn fixed to the patient""s teeth. Interarch devices can either be passive or active. An example of an active interarch device is shown in my U.S. Pat. No. 5,711,667 which is incorporated by reference as though fully set forth.
However, a problem exists with these interarch devices. When opening the mouth, an interarch device that is loosely attached to the braces about the archwire in the lower anterior region of the teeth tends to rotate upwardly in the front of the mouth toward the upper teeth. FIG. 1 illustrates how the anterior end of the pushrod of an interarch device rotates upward and into the bite when the patient opens his/her mouth. Element 11 is a cylinder and 13 is the long arm of the pushrod. Element 15 is the anterior connection of the pushrod which in this case is a hook formed in the end of the pushrod which encircles the lower archwire 17. With the structures in this position, the patient can bite on the arm of the attachment hook when he/she closes his/her mouth. This occurs because the attachment point is offset from the body a sufficient distance to enter the patent""s bite when a common hook or loop attachment is employed. A bend, usually 90 degrees or less, is employed to place the axis of the hook parallel to the axis of the archwire to permit sliding movement along the archwire. However, these mechanical relations allow the unrestricted rotation about the archwire which creates the unwanted motion of the end of the pushrod into the patient""s bite.
This tendency to rotate into the bite is increased when the loosely attached interarch device is active due to its having a push-spring such as an open coil spring incorporated into its design. In an active telescoping device, the nature of the activated spring is to tend to return to a state of least spring energy, (i.e. greatest length). In the case of prior art telescoping interarch devices this most extended state occurs when the device has rotated upwardly at its anterior connection. Thus, the spring forces the arm of the hook or loop attachment structure to rotate up into the area of the patient""s bite.
The tendency of the interarch device to rotate upward in the anterior region can be avoided at present by two means: either rigidly fixing the anterior connection, or by moving the anterior connection point lower than the lower teeth by connecting it using an additional bypass wire that is lower than the level of the braces in the direction of the gums. In this case, when the device rotates, it is still at a level lower than the lower teeth thereby avoiding the bite. Although rigid fixation prevents the appliances from rolling into the bite, it usually limits the patient""s range of jaw motion. In addition, rigid fixation usually requires many more parts and complicated design features that make both manufacturing and installation in the patient""s mouth more difficult.
A loose attachment of the orthodontic appliance described above is preferred because it allows for greater freedom of motion. However, as noted above, a loose attachment encourages push-spring loaded interarch appliances to rotate into the bite because the compressed spring tends to naturally return to its uncompressed normal state (least stored energy) and thus has a tendency to move to a position of greatest extension in the unwanted upward direction. Therefore, a second solution as previously mentioned is to utilize a bypass wire which lowers the connection point of the attachment. Thus, when the interarch device does rotate, it rolls into the side of the teeth instead of the bite and this prevents the patient from biting it. But unfortunately, adding a bypass wire increases the number of parts that must be manufactured and installed. In addition, the bypass wire increases the chance of breakage by the patient when chewing and it makes the appliance more intrusive by adding to its overall bulk.
There is therefore a need in the art for an improved attachment that allows an interarch orthodontic device to be loosely attached to the patient""s upper and lower teeth that is simple to manufacture and to install and does not allow the device to interfere with the patient""s bite.
The present invention consists of the addition of a recurve bend located adjacent to a shepherd""s hook or loop attachment of a telescoping or rigid interarch orthodontic device that makes the anterior end of the device rotate downwardly rather than upwardly when force is applied. When the device is installed onto the patient""s braces the additional recurve bend in effect creates a rocker arm. As the jaws move, a cam-action against the archwire is produced that does not allow the attachment end of the device to move above the horizontal plane of the bite as the connection rotates.
For the recurve bend of the invention to create the beneficial desired cam-action, the bend should be a minimum of 120 degrees from the longitudinal axis of the interarch orthodontic device in the backward direction. As the degree of this backward curvature approaches 210 degrees, the recurve bend further positions the hook attachment pivot point below the axis of the body of the interarch device in the vertical plane. This further prevents the appliance from rotating into the bite because the position of greatest possible extension is approached as the device rotates downward instead of upward at the anterior end of the bite. An optional second offset bend in the lateral plane of no more than 60 degrees creates a second beneficial cam effect in the lateral plane.
More specifically, the applicant has invented an interarch orthodontic device for a person comprising a body including a cylinder having first attachment means affixed to an upper tooth at one end and an opening at an opposite end. A telescopic rod is slidably retained within a bore of the cylinder and the distal end of the rod extending from the cylinder includes second attachment means which provide pivotable hook-type attachment about an archwire affixed to an orthodontic appliance which in turn is affixed to a lower tooth. A recurve bend located on the rod lies adjacent the lower archwire attachment so that when a person""s jaws are moved toward the closed position, contact between the sides of the hook and the archwire hold the rod away from the person""s bite. Spring means may be included either surrounding the cylinder and rod or within the cylinder bore providing a resilient force bearing against the end of the rod. The recurve bend is preferably greater than 135 degrees. The posterior end of the rod can include a substantially cylindrical cavity which receives the spring means. The interarch orthodontic device may be oriented so that the attachment means at the end of the rod are oriented either anteriorly or posteriorly. Other details of the invention will be apparent from the following drawings and description of the preferred embodiment.